1. Field of the Invention
This invention relates to a process and system for the treatment of hydrocarbon-contaminated soil.
2. Description of the Prior Art
For some time now, the art has been faced with the problem of the treatment of hydrocarbon-contaminated soils. Such a problem relates to soil which may have been contaminated through intentional or accidental spills of petroleum oils, hydrocarbon solvents or other, semi-volatile or non-volatile organic materials. Such contaminants may extend over large tracts of land and may directly or indirectly, e.g. through subsequent contamination of an underlying aquifer, constitute an extreme threat to wildlife, vegetation or human health. Conventional methods, e.g. land farming are not very suitable.
Another problem relates to oil well sumps. Oil well sumps are artificial pits used as dump sites for all kinds of liquid and viscous wastes. The physical consistency of the sump varies according to the random materials dumped. Typically, however, in the absence of a water layer, the consistency is pasty. Inasmuch as sumps create traps for wild fowl, there is an increasing demand for elimination of sumps, especially those not being commercially used. In addition, they are unsightly. The traditional treatment has been to dump and mix dirt into the sump and thereby soak up sufficient of the oil until the dirt-sump material can be moved by conventional equipment. The mixture is then spread to dry. This treatment has not been acceptable because the mixture bleeds oil and chemicals. Over months and years, this dirt-sump mixture oozes oil and becomes almost as objectionable as the original oil sump. This unsatisfactory type of treatment has called for an improved solution to the ecological problem of sump elimination.
The increasing use of hydrophobic substances, e.g. oils and oily substances, as well as macromolecular substances, has created new problems which arise mainly out of the handling of these substances. Particularly, the use of old oil, heating oils, lubricating oils and diesel fuels often leads, either intentionally or through negligence, and often due to emergency situations, to dangerous contamination of the environment.
There are a number of methods for rendering harmless such oils or oily substances which, in a single phase or in multiple phase systems, entail an endangerment of the environment. For example, oil can be chemically reacted by being burned, for example, or biologically degraded. The combustion method used frequently in combatting oil damage results in considerable air pollution if the burning is performed in the open rather than in expensive combustion apparatus.
The use of adsorbents solves such problem only when the oil can be fixed with them in such a manner that it is chemically unaltered but is encapsulated or otherwise isolated or is accessible to biological degradation and no longer constitutes any danger to the environment. With the known adsorptive agents, e.g. activated charcoal, kieselguhr or bentonite, waste oil, for example, can be adsorptively bound only with difficulty. Large amounts of oil may cement the adsorptive agent, especially in the case of high-viscosity oils, making further processing difficult.
It has furthermore been proposed in various ways to treat porous mineral substances with hydrophobic substances for the purpose of improving their adsorptive characteristics. In this manner hydrophobic waste substances can be preferentially bound, while the water is no longer primarily absorbed. In such adsorptive agents, such as hydrophobized pearlite, however, the absorptive capacity is greatly reduced, since the mineral starting material is partially sealed by surface treatment with hydrophobizing substances, so that the inner cavities are no longer accessible.
It is particularly important that the substances which are adsorptively bound by the known processes are so fixed on the adsorptive agent that they no longer constitute any danger to the environment.
In addition to the general, mainly unsatisfactory procedures for the problems of disposal of such wastes discussed above, the patent literature has purported to provide solutions to these problems. For example, one solution to the problem was said to be provided in U.S. Pat. No. 3,720,609, patented Mar. 13, 1973 by C. L. Smith et al. That patent provided a procedure whereby waste sludges containing small amounts of certain types of reactive materials were treated by adding, to such sludges, materials capable of producing aluminum ions, lime and/or sulfate-bearing compounds to produce a composition containing sulfate ions, aluminum ions and equivalents thereof, and calcium ions and equivalents thereof. Over a period of time such compositions hardened by the formation of calcium sulfo-aluminate hydrates.
Another solution to the problem was said to be provided in U.S. Pat. No. 4,028,240 patented Jun. 7, 1977 by F. Marchak Jr. That patent provided a procedure whereby lime, preferably as calcium oxide, was mixed with the contents of sumps, e.g. oil well sumps. The calcium oxide reacted with the materials present and also dehydrated the contents of the sump, causing the sump contents to stiffen.
Yet another solution to this problem was said to be achieved in U.S. Pat. No. 4,018,679 patented Apr. 19, 1977 by F. Boelsing. That patent provided a method for rendering an oil waste material harmless by mixing an alkaline earth metal oxide with a surface active agent which delayed reaction between the alkaline earth metal oxide and water. The mixture was combined with oily material, e.g. a sludge or an oil-contaminated soil. The alkaline earth metal oxide charged with the waste material was reacted with approximately the stoichiometric amount of water to convert the alkaline earth metal oxide to the hydroxide. The alkaline earth metal oxide was preferably calcium oxide and advantageously it was also mixed with a hydrophobizing agent prior to mixture with the oily waste material.
In the patent to Boelsing described above, the composition used was preferably prepared by blending lime with a solid fatty acid (in particular, a commercial grade of stearic acid commonly called stearin) by slowly adding the acid to coarse lime as it was subjected to the process of fine-grinding. The purpose of this operation was to render the lime hydrophobic, thereby delaying its hydration reaction with water and permitting it to be intimately mixed with contaminated soil by mechanical means. Subsequent hydration then resulted in an extremely fine and uniform dispersion of the contaminants, hydrated lime and soil. In practice, however, the purpose of that invention was not always achieved to its optimum.
Nevertheless, the procedures outlined above did not provide a total answer to the problem of effective treatment of hydrocarbon-contaminated soil.